Electrical apparatus



June 18, 1946. L, H. BEDFORD ELECTRICAL APPARATUS Filed Sept. 28, 1943 INV T0 Leslie Herbert B 01' atented June 18, 1946 all ELECTRICAL APPARATUS Leslie Herbert Bedford, London, England assignor to A. C. Cossor Limited, London, England, a

British company Application September 28, 1943, Serial No. 504,110

In Great Britain October 7, 1942 9 Claims. i

This invention relates to alternating current circuits comprising iron-cored inductive devices. It is particularly applicable to the purpose of eliminating errors in alternating current measuring and calculating apparatus which arise from the nonlinear magnetic saturation characteristics of iron-cored inductive devices employed therein.

One aspect of the invention is directed to the problem of producing, in such a device, an alterhating magnetic flux which varies proportionally in amplitude with, and keeps in phase quadrature with, an alternating input voltage. The circult according to this aspect of the invention comprises an amplifier having its output applied to a primary winding of the inductive device, means comprising a secondary winding linking the magnetic iiux produced by said primary winding to develop a feedback voltagesubstantially in phase quadrature with said flux and substantially proportional in amplitude thereto, and nearly equal to the input voltage, and means to inject said feedback voltage degeneratively into the input circuit of the amplifier.

Another aspect oi the invention isdirected to the problem of producing, from an iron-cored inductive device, a secondary alternating voltage which varies proportionally in amplitude with, and keeps in phase with, an alternating input voltage, The circuit according to this aspect of the invention comprises an amplifier having its output applied to a primary winding on said inductive device, means comprising a secondary winding on said inductive device to develop a feedback voltage nearly equal to the input voltage, and means to inject said feedback voltage degeneratively into the input circuit of said amplifier.

The invention is particularly applicable to the problem of exciting a low frequency iron cored. goniorneter, sometimes lrnown as a magslip resolver. This device will normally comprise relatively rotatable stator and rotor elements, each having an iron core and each having two windings arranged 90 apart. When a constant alternating voltage is applied to one of the windings on one element, say the stator, the voltage produced in. one oi the windings on the other element (the rotor) is proportional to the sine oi the angle to which the rotor is set relatively to tional voltages will he produced in the rotor windirgs, proportional respectively to the cosine and sine or the said angle of setting. When the amplitudes of the voltages applied to the stator windings are varied, the non-linear magnetic characteristics of the iron cores will produce variations of phase angle with amplitude, and the voltages produced in the rotor windings will not vary in exact proportion with the voltages applied to the stator windings. A principal feature of the invention is the avoidance of this difficulty.

In the application of the invention to magslip resolvers, the secondary windings employed to develop the feedback voltages will be auxiliary windings arranged on the some element (stator or rotor) as the primary windings-that. is to say, the windings which are used to excite the resolver. Where two primary windings apart are employed, each of the auxiliary secondary windings will be in space-phase with the primary winding into the circuit of which it provides feedback.

Further aspects of the invention will be apparent from the accompanying claims.

The accompanying drawin shows a circuit diagram of an electrical calculating apparatus emhodying the invention.

The purpose of this apparatus is to develop two output alternating voltages U1 and U2, the amplitudes or which are related to two input voltages V1 and V2 in accordance with the laws:

the auto-transformers may be continuously and.

independently moved, either manually or automatically, so that voltages V1 and V2, while re maining in phase with each other, are continuously varied in amplitude in proportion to two independently varying magnitudes a: and :1 which they will then continuously represent.

The primary windings E and l of the magslip resolver are oath. arranged on the stator and are disposed. 9i) apart so that no voltage is pro duced in either by the flux which is induced by the excitation of the other. The ordinary secondary windings El and t are both arranged on the rotor and are similarly disposed at an angle of 90 to each other. Voltages are excited in these secondary windings by the fluxes which are induced in the iron cores by excitation of the primary windings 6 and 1. The voltages U1 and U2 excited in these windings B and 9 respectively are approximately given by:

where Va and V1 are the alternating voltages across windings 6 and I. These equations would be exactly true only in the case of zero resistance in the primary windings and I; in practice the magnetizing currents in these windings cause resistance drops which introduce errors.

In the arrangement according to the invention, auxiliary secondary windings I0 and II are provided. These are placed on the stator co-axially with primary windings 6 and 1 respectively and are employed to provide degenerative feedback voltages substantially proportional to, and in quadrature with, the fluxes actually induced in the two perpendicular axial directions. Windings 6 and I0 may be wound together as a bifilar winding, and similarly may windings l and I I.

The primary windings B and l are excited from the input alternating voltages V1 and V2 through thermionic valve amplifiers l2 and 13. These are shown as modified cathode follower ampliflers; but other forms of amplifier may alternatively be used, such as those in which the outputs are developed across anode loads. If cathode loads are chosen, the primary windings 8 and i may be directly connected to form these loads provided that their impedances are sufficiently high. It will normally be preferred, however, to connect them as cathode loads through the medium of output transformers as shown at 23 and 24, which will also serve to eliminate direct current from the primary windings 6 and T. In any case, the loads are preferably tuned to the frequency of source 22 by parallel condensers l4 and IS.

The auxiliary secondary windings IO and II are connected back degeneratively'to the input sides of amplifier I2 and Hi. The voltages fed back from the auxiliary secondary windings 'HI and H in opposition to input voltages V1 and V2 are nearly equal in amplitude and phase to the said input voltages. If the windings l0 and If are suitably proportioned for this purpose they may be directly connected into the input circuits, but they are shown as connected through voltage transformation devices l6 and I1 which will have the correct transformation ratio to achieve this end. Devices l6 and I! may be voltage step-up or step-down transformers or autotransformer having high impedances, and may be provided with means for adjusting their ratios. Alternatively they may be resistance networks or thermionic valve amplifiers.

The vector difference voltages between (a) the voltages V1 and V2 tapped from potentiometers 20 and 2|, and (b) the output voltages from devices I6 and H, are applied a inputs to amplifiers l2 and I3 preferably through the medium of voltage step-up devices l8 and IS. The greater the voltage step-up provided by devices l8 and I9 and amplifier l2 and II, the more accurate will be the compensation for errors'due to magnetizing currents in the magslip resolver 5.

Devices l8 and I! may be transformers, but

will preferably be high gain thermionic valve amplifiers. Care must, of course, be taken that no phase reversals shall occur in either of these devices at any frequencies within the range for which the gain of the feedback system exceeds unity; otherwise the system wil1 be unstable.

Whatever the nature of devices l6 and i1 and of devices l8 and I9 that may be selected, it is important that auxiliary secondary windings Ill and II shall not be appreciably loaded. In some applications of the invention it may also be important that the sources of input voltages V1 and V2 shall not be appreciably loaded.

If the voltage of the alternating current source 22 is constant, the output voltages U1 and U2 may be measured by simple voltmeters. If, however, there is a possibility of variation of the voltage of the supply source, it is preferable that voltages U1 and U2 shall be measured by nulling against voltages tapped off from potential dividers connected across source 22. The arrangement accordin to the invention insures that the voltages U1 and U2 are both in phase with the voltage of source 22.

In the arrangement shown in the drawing, the rotor windings 8 and 9 of the magslip resolver 5 are respectively connected for this purpose through null meters 25, 26, acros tapped off portions of variable ratio auto-transformers 21 and 28, If the tappings of auto-transformers 21 and 28 are continuously moved so as to maintain null readings on meters 25 and 26, then the ratios of transformers 21 and 28, which may be measured by suitable scales, will continuously represent (m cos 0-y sin 9) and (a: sin 0+y cos 0) tude of said input voltage and the adjusting angle between said primary and secondary windings, an amplifier interposed between said input and said primary winding, and a tertiary winding for said transformer connected to the input of said amplifier and arranged to develop a degenerative feedback voltage substantially counteracting said input voltage.

2. An electric system having an input and an output and comprising a transformer between said input and output having at least one iron-- cored primary and secondary winding rotatably adjustable relative to each other, means to apply an alternating input voltage of constant frequency and varying amplitude from said input to said primary winding to derive an alternating voltage of like frequency from said output varying both in accordance with the amplitude of said input voltage and the adjusting angle between said windings, an amplifier interposed between said input and said primary winding, a tertiary winding for said transformer connected to the input of said amplifier and arranged to develop a degenerative feedback voltage substantially counteracting said input voltage, and means to tune said primary winding to said constant frequency.

3. An electric system having an input and an vutput and comprising a transformer between aid input and said output having at least one ron-cored primary and secondary winding roatably adjustable relative to each other, means 0 apply an alternating input voltage of constant requency and varying amplitude from said input 0 said primary winding to derive an alternating oltage of like frequency from said output vary ng both in accordance with the amplitude of :aid input voltage and the adjusting angle be- ,ween said windings, an amplifier interposed be- .ween said input and said primary winding, a ertiary winding for said transformer connected 0 the input of said amplifier and arranged to levelop a degenerative feedback voltage substan- ;ially counteracting said input voltage, and a conienser in parallel to said input winding to tune raid input winding. to said constant frequency.

4. An electric system having an input and an iutput and comprising a transformer between said input and output having a stator, a rotor,

:tator and rotor windings associated therewith,

means to apply an alternating input voltage of :onstant frequency and varying amplitude from said input to said stator winding to derive an alternating voltage of like frequency from said output varying both in accordance with the amplitude of said input voltage and the adjusting angle between said stator and rotor, an amplifier interposed between said input and said stator winding, and a tertiary winding upon said stator connected to the input of said amplifier to develop a degenerative feedback voltage substantially counteracting said input voltage.

5. An electric system having a pair of inputs and a pair of outputs and comprising a transformer having pairs of iron-cored primary and secondary windings, the windings of each pair being displaced by predetermined fixed angles and the windings of one pair being rotatabiy adjustable relative to the windings of the other pair, said secondary windings being connected each to one of said outputs, means to apply a pair of alternating input voltages of like and constant frequency and relatively varying amplitude each from one of said inputs to one of said primary windings to derive alternating voltages from said outputs of like frequency and amplitudes varying both in accordance with the amplitude of the respective input voltage and the angular adjusting position between said primary and secondary windings, amplifiers interposed, between said inputs and the respective primary windings, and a pair of tertiary windings for said transformer connected each to the input of its respective amplifier and arranged to develop degenerative feedback voltages substantially counteracting said input voltages.

6. An electric system having a pair of inputs and a pair of outputs and comprising a transformerhaving pairs of iron-cored primary and secondary windings, the windings of each pair be-' ing displaced by 90 and the windings of one pair being rotatably adiustably to varying angles 0 relative to the windings of the other pair, said secondary windings being connected each to one of said outputs, means to apply a pair of alternating input voltages V1 and V: of like and con-' stant frequency andrelatively varying amplitude each from one of'said inputs to one of said primary windings to derive alternating voltages U1 and U: from said outputs of like frequency and having amplitudes equal to V1 cos 0-V: sin 0 and V1 sin 0+V2 cos 0, respectively, amplifiers interposed between said inputs and the respective primary windings, and a pair of tertiary windings for said transformer connected each to the input of the respective amplifier and arranged to develop degenerative feedback voltages substantially counteracting said input voltages.

'7. An electric system having a pair of inputs and a pair of outputs and comprising a transformer having pairs of iron-cored primary and secondary windings, the windings of each pair being displaced by and the windings of one pair being rotatably adjustable to varying angles 0 relative to the windings of the other pair, said secondary windings being connected each to one of said outputs, means to apply a pair of alternating input voltages Vi and V2 of like and constant frequency and relatively varying amplitude eachamplifier and arranged to develop degenerative I feedback voltages substantially counteracting said input voltages, and means to tune said primary windings to said constant frequency.

8. An electric system having a pair of inputs and a pair of outputs and comprising a transformerhaving a stator and a rotor, a pair of stator windings angularly displaced by 90, a pair of rotor windings also angularly displaced by 90;- said rotor windings being connected each to one of said outputs, means to apply a pair of alternating input voltages of like and constant frequency and relatively varying amplitude each from .one of said inputs to one of said stator windings to derivealternating voltages from said outputs of like frequency of amplitude varying both in accordance with the amplitude of the respective input voltage and the angular position between said stator and said rotor, amplifiers interposed between said inputs and the respective stator windings, and a pair of tertiary windings upon said stator connected each to the input of the respective amplifier and arranged to develop degenerative feedback voltages substantially counteracting said input voltages,

9. An electric system having a pair of inputs and a pair of outputs and comprising a transformer having a stator and a'rotor, a pair of stator windings angularly displaced by 90, a pair of rotor windings also angularly displaced by 90, said rotor windings being connected each to one of said outputs, means to apply a pair of alternating input voltages of like and constant frequency and relatively varying amplitudes each from one of said inputs to one of said stator windings to derive alternating voltages from said outputs of like frequency of amplitude varying both in accordance with the amplitude of the respective input voltage and the angular position between said stator and said rotor, amplifiers interposed between said inputs and the respective stator windings, a pair of tertiary windings upon said stator connected each to the input of the respective amplifier and arranged'to develop degenerative feedback voltages substantially counteracting said input voltages, and a pair of condensers each in parallel to one of said stator windings to tune said stator windings to said predetermined frequency.

LESLIE HERBERT BEDFORD. 

